Scott needs to win the event and have world No.1 Tiger Woods finish worse than fifth to take top spot in the rankings.

Woods, who is playing with Scott, is two over to be tied 47th in the 68-man elite field.

The 14-time major winner bogeyed the fourth and 10th holes and is yet to make a birdie a week after withdrawing from the Honda Classic with back spasms.

"I felt a lot better today," Woods said.

"Tomorrow should be a long day for all of us. Hopefully tomorrow I can get back out there in the morning, play well and work back to even par by the end of the first round then shoot a low one in the afternoon."

Scott is joined by six others just a shot off the lead, including fellow Masters winners Zach Johnson and Charl Schwartzel.

Earlier, Australia's world No.4 Jason Day withdrew with a thumb injury before starting his round.

After some soreness in his warm-up, Day pulled the pin with a grade-one ulnar collateral ligament strain in his left thumb.

Fresh from winning the WGC Match Play Championship two weeks ago, the 26-year-old decided not to risk further injury before next month's Masters.

Brett Rumford had a sensationally poor start to his tournament, carding a sextuple-bogey 11 on his opening hole.

Starting on the par five 10th, Rumford hit three tee balls into a large lake before finally finding dry land on the fourth attempt.

He now finds himself eight over through 12 holes.

The other Australian, Scott Hend, was one of just six players to finish and shot an even-par 72.